The present invention relates to a scanning electron microscope and, more particularly, to a scanning electron microscope which is equipped with proper means for controlling the moving speed of a specimen stage.
Heretofore, many scanning electron microscopes have been used in medical and biological fields mainly with a view to observing the microscopic shapes of specimens. In recent years, however, the scanning electron microscopes have rapidly come to be used as an apparatus for observing the patterns of IC, LSI and so on in the semiconductor industry. In accordance with this use, it has become necessary to set the two-dimensional coordinates, i.e., X- and Y-coordinates of the specimens because specimens of IC, LSI, etc., have many identical patterns on their wafers or chips. That necessity cannot be coped with any more by the prior art manual movement of the specimen stage. In view of this, therefore, the specimen stage movement is being executed with high accuracy in response to electric signals by using a pulse motor or servomotor. As is disclosed in Japanese Patent Laid-Open No. 55-95113, there is an example in which the movement of the specimen stage is executed by electric control using a pulse motor.
In case the specimen stage movement is applied to the scanning electron microscope (which will be shortly referred to as "SEM"), however, it should be noted that the magnification of the scanning electron microscope varies over a wide range of about 20 to 500,000 times. This means that the moving speed of the specimen stage is low for a small magnification but high for a large magnification on the SEM image on a cathode ray tube (which will be shortly referred to as "CRT", as customary) being observed, if it is kept constant, thus raising a problem that the SEM cannot operate to observe the SEM image and execute location of a point while moving the specimen stage bit by bit.